Nothing wrong with a mega-church, if it is in accordance with God's Word, particularly per Apostle Paul's Epistles. And since it is a large congregation, it ought to be able to afford having a Bible scholar of the Hebrew and Greek as a Teacher as their sole duty, for that was one of the main jobs of the Hebrew priest, to go through all of God's Word line upon line, reading it, and giving the people the meaning. That means chapter by chapter, line upon line Bible teaching. Where can one find that today? Some churches, but not that many.
Small country churches are pretty much left on their own, they will have preachers picked from their organization denomination if they belong to a denomination. And most often, they only fit the evangelist role, which is not a scholarly Bible teacher, but one mainly called to preach The Gospel. This is why those churches struggle when it comes to teaching the congregation that had already heard and believed The Gospel, many, many years before, and over time are supposed become Bible teachers themselves (Heb.5).
There's a mega-church near my sister's house. It's buildings are HUGE. I know several brethren that go there. The main thing I get from them, is the church attracts all this entertainment from Country music stars out of Nashville. It's like they are using entertainment to attract followers. I don't know if they have Biblical scholar teachers, because none of that was mentioned to me, only how great the music and entertainment was.